Grief not adding to Smite Damage

Maybe i am just stupid, but i was to understand that Grief would add to my smite damage. Yet when i equip it, my damage doesnt apear to go up at all in the stat window. Is this a bug or does grief not add to smite damage at all?

I have searched all over, and from what i can find, grief is one of the main weapons for a smite paladin. If it doesnt add damage...then whats the point of it?